1. Field of the Invention
Exemplary embodiments of the present invention relate to a communication system; and, more particularly, to a backward-wave oscillator using a metamaterial waveguide.
2. Description of Related Art
In general, a backward-wave oscillator is a device which allows electronic beams to enter a beam tunnel so as to generate microwaves and terahertz electromagnetic waves. The backward-wave oscillator includes a waveguide. The phase velocity of an unloaded waveguide is higher than or almost equal to the light velocity, but the phase velocity of electronic beam is lower than the light velocity. Thus, it is difficult to combine electronic waves and electronic beams using the unloaded waveguide. Therefore, a periodic-structure waveguide of which the phase velocity is lower than the light velocity is used as the waveguide of the backward-wave oscillator. The backward-wave oscillator causes the electronic waves and electronic beams to interact in the periodic-structure waveguide.
The backward-wave oscillator using the periodic-structure waveguide acquires a point at which the phase velocity of the periodic-structure waveguide coincides with the phase velocity of electronic beams, which is lower than the light velocity, in a spatial harmonic region. The backward oscillator generates microwaves and terahertz electromagnetic waves through the interaction between the periodic-structure waveguide and the electronic beams at the frequency at which the two phase velocities coincide with each other.
The conventional backward-wave oscillator must use the slow wave dispersion characteristic of the periodic-structure waveguide due to the phase velocity of electronic beams, which is lower than the light velocity. Thus, the conventional backward-wave oscillator must use backward waves corresponding to the spatial harmonic region.